The present invention relates to electron beam radiation therapy (radiotherapy) treatment of tumors and the like and in particular to a treatment planning tool providing improved dose profile for electron beam radiation therapy machines.
Radiotherapy treats tissue with high-energy radiation. The amount of radiation and its placement must be accurately controlled to ensure both that the tumor receives sufficient radiation to be destroyed and that the damage to the surrounding and adjacent non-tumorous tissue is minimized.
External source radiotherapy may use high-energy radiation such as photons or electrons. In electron beam radiotherapy, a source of electrons, for example from a linear accelerator, may be directed toward the patient at a given angle and collimated to a given beam size (cone size). The energy of the electrons may be set, typically to one or more discrete energy levels of 4, 6, 9, 12, 15, 16, 18, 20 or 22 MeV. Typical cone sizes include 4×4, 6×6, 10×10, 15×15, 20×20, and 25×25 cm. The cumulative flux and hence the dose may be controlled by controlling the monitor units (“MU”) of the radiation therapy machine through direct control of the linear accelerator current and/or control of the exposure time.
Electrons have a particular advantage in the treatment of some superficial cancers such as skin, breast, head and neck tumors, and intraoperative surgical procedures in that they provide rapid falloff as a function of penetration depth. Control of the depth of falloff of the electron beam may be provided by use of a customized bolus, being typically a water equivalent or tissue mimicking material placed on the patient's skin to provide some initial interaction with the electrons before the electrons reach the region targeted for treatment.
Standard electron beam radiation therapy machines are essentially “single-beam” devices providing a single, essentially constant and uniform electron beam. More sophisticated “intensity modulated” radiation treatment machines and treatment planning systems have been proposed in which the electron beam is divided into “beamlets”, each separately modulated by intensity and/or energy. A complex inverse treatment planning technique, for example, a Monte Carlo based algorithm, would be used to optimize the fluence and energy of the many beamlets over multiple treatments. Such equipment and the necessary planning tools are not available in most clinical settings.